1. Technical Field
This Specification relates generally to switching regulators (switched mode power supplies) for isolated-load applications, such as may be used as a switching regulator for an isolated LED (string) load.
2. Related Art
One application for switching regulators (switched mode power supplies/converters or SNAPS) is to provide a regulated load current for an LED string. Such LED switching regulators may be used in DC/DC converter applications, but are commonly used in off-line AC/DC applications (i.e., where the power input to the switching regulator is from an AC power line). In such off-line AC/DC applications, and some DC/DC applications, the load is required to be isolated from the AC line or other source of input power.
For off-line isolated applications, an LED switching regulator is commonly based on a flyback converter/transformer with primary side switching and control. The regulation loop includes a primary side controller that provides gate drive for the switching transistor, converting AC voltage/current from the AC power line into a regulated, substantially constant secondary side current supplied to the LED load.
Implementing a switching regulation loop requires that the primary side controller directly or indirectly receive some indication or representation of secondary side current. A direct approach is to use direct secondary side current sensing with secondary-to-primary side feedback across the isolation transformer to the primary side controller, such as by means of an opto-coupler.
To eliminate the need for an opto-coupler or other means of secondary side sensing/feedback, an alternative approach is to use information detected/sensed on the primary side as a representation of secondary side current. That is, the primary side controller receive input(s) from detecting/sensing primary side operational parameters, which are used to control transistor switching, establishing an primary side regulation loop to control primary side power conversion and provide regulated, substantially constant secondary side current through the LED load.
While this Background information is presented in the context of a switching regulator for LED applications, this Specification is not limited to such applications, but is more generally directed to switching regulators (SMPS converter/controller) applications in which an isolated load requires a regulated supply current.